FIG. 10.3.2-3 of Hewlett-Packard publication "Optoelectronics, Fiberoptics Application Manual", 1981, discloses a receiving circuit in which an output signal that is both differential and symmetrically grounded is tapped via two comparators which specify a receiving threshold. Valid signals which exceed the prescribed receiving threshold are electrically isolated from the line side by means of an optocoupler configuration and are transmitted to the operating side of the receiving circuit where they are regenerated by means of a bi-stable, flip-flop circuit. The receiving level recording signal is also generated only on the operating side from the symmetrically grounded, differentially transmitted output signal. This occurs because the two optocouplers' output signals of the optocoupler configuration, via which the symmetrically grounded output signal is transmitted in case of sufficient receiving level, are logically linked via a NAND gate so that the receiving level control signal is present on its output.
The disadvantage of such a receiving circuit where the receiving level control signal is generated only on the operating side, is that the received data does not always appear only after exceeding a receiving threshold. This is due to distortion of the received input signal which is caused along the transmission route and under some conditions, can lead to difficulties in the evaluation of the received data.
Consequently, it is an object of this invention to provide a receiving circuit which allows error free regeneration of received data, even where the received input signal possesses distortions.